Category Archives: Brassica Vegetables

Downy mildew of brassica vegetables

Downy mildew of brassicas (Hyaloperonospora parasitica syn. Peronospora parasitica) is a fungal-like oomycete that can be devastating in cooler, wet weather. While the ideal temperature for downy mildew development is 8-16˚C it can infect in temperatures outside that range. Prolonged leaf wetness due to fog, dew, or evening irrigation can create ideal conditions for the pathogen to develop.

Downy mildew is most devastating on Continue reading Downy mildew of brassica vegetables

Disease and Insect Update – July 13, 2017

Insect Degree Days

Weather Station Location Onion Maggot Seedcorn Maggot Cabbage Maggot Carrot Weevil Carrot Rust Fly Aster Leafhopper
(base 4°C) (base 4°C) (base 6°C) (base 7°C) (base 3°C) (base 9°C)
Harrow 1265 1265 1044 938 1380 746
Ridgetown 1153 1153 937 838 1268 660
Delhi 1125 1125 910 813 1237 636
Goderich 973 973 775 684 1076 533
Guelph 928 928 735 646 1034 492
Bradford* 987 987 795 708 1086 547
Kemptville 969 969 786 700 1069 544
Sudbury 754 754 597 525 845 394

*Bradford weather, degree day data and information courtesy of the University of Guelph – Muck Crops Research Station

Summary

Cabbage, onion and seedcorn maggot fly activity should be beginning to increase from Norfolk across to Lambton and south. Most of the province is in-between generations currently but should start seeing the next generation emerge in the next few weeks depending on weather.

For carrot weevil we are now well past the degree day threshold for 90% oviposition across the province. This year we will be monitoring for the presence of a possible 2nd generation of carrot weevils. If you think you are having late season carrot weevil issues, please contact Dennis (dennis.vandyk@ontario.ca).

We have reached the DD threshold for carrot rust fly in Harrow only. The rest of the province should be between generations currently.

Aster leafhoppers adults are now present across the province.

Disease Forecasting

Onion Downy Mildew (DOWNCAST disease forecasting model):
In Bradford, conditions have not been conducive to sporulation so risk of downy mildew is low to moderate.
In Lambton county, sporulation infection periods (SIP) have been accumulated from July 2-5 and then again on July 12 meaning conditions and risk is high in transplant onions and moderate to high in seeded onions.

Late Blight:
Late blight DSVs are accumulating quickly in most areas of the province.
Late blight on potatoes has been confirmed in the Simcoe/Durham county region but the risk remains high across the province. Growers should be applying late blight specific fungicides along with a broad-spectrum fungicide like chlorothalonil (Bravo, Echo), metiram (Polyram) or mancozeb (Manzate, Penncozeb, Dithane).

Check OnPotatoes for up to date late blight risk information and USAblight for currently reported late blight incidence in the Great Lakes region.

Crop Updates

Onions: Earliest direct seeded onions have six true leaves while the majority are at the four to five leaf stage. Stemphylium leaf blight, purple blotch, onion smut and Botrytis leaf blight has been detected in Ontario. See the Stemphylium leaf blight article in a previous OnVegetables post for more information.

Garlic: Leaf dieback has been seen in multiple areas with Fusarium basal rot and bulb and stem nematode. Carefully inspect the basal plate and look for fungal growth or rot on the stem. For confirmation, send suspect cloves to a certified pest diagnostic clinic for bulb and stem nematode extraction. Leek moth has been identified in pockets of Southwestern Ontario.

Brassica: Cabbage maggot is active and severely infested plants may wilt in hot weather. Wilt can also be caused by clubroot, a soil-borne pathogen infecting the roots and causing club-like symptoms. A clubroot survey is underway; please contact travis.cranmer@ontario.ca for more information if you find clubroot in your field. Swede midge has also been reported throughout Southwestern Ontario and is affecting the meristems later seeding dates of multiple brassica crops. Continue to scout for flea beetles, diamondback moth, cabbageworm, aphids, thrips and tarnished plant bugs.

Celery: Tarnished plant bugs have been detected in Thedford and the Holland Marsh. Scout for damage from carrot weevils laying eggs.

Below are the various insect DD thresholds for reference.

Thresholds

Use these thresholds as a guide, always confirm insect activity with actual field scouting and trap counts.

Degree Days
1st generation 2nd generation 3rd generation
Onion Maggot 210 1025 1772
Seedcorn Maggot 200 600 1000
Cabbage Maggot 314-398 847-960 1446-1604
Carrot Rust Fly 329 – 395 1399-1711 n/a
Carrot Weevil 138 – 156 Egg laying (oviposition) begins
455 90% of the egg-laying (oviposition) is complete
Aster Leafhopper 128 Overwintering eggs hatch
390 Local adult emergence

Ontario DD Map July 13

Cabbage Maggot; An old pest with limited options

The cabbage maggot (Delia radicum) is the larvae stage of the cabbage root fly which can cause severe damage to all Brassica crops. The adult cabbage maggot is a fly that is about half the size of a house fly and is grey in colour.

In the early spring, cabbage maggot flies emerge from the soil and the females lay small, white eggs ~2-10 cm below the soil line. Depending upon the temperature, eggs hatch 3-7 days later as larvae that immediately start boring Continue reading Cabbage Maggot; An old pest with limited options

Insect Pest and Crop Degree Day Update – May 26

Ontario DD Map May 25

Insect Degree Days

 

Weather Station Location Onion Maggot Seedcorn Maggot Cabbage Maggot Carrot Weevil Carrot Rust Fly Aster Leafhopper
(base 4°C) (base 4°C) (base 6°C) (base 7°C) (base 3°C) (base 9°C)
Harrow 468 468 342 285 535 189
Ridgetown 408 408 288 237 475 155
Delhi 391 391 271 222 455 141
Goderich 308 308 206 164 363 108
Guelph 284 284 186 145 342 87
Bradford*  318 318   205 172  369  112
Kemptville 304 304 217 179 356 119
Sudbury 168 168 105 82 210 47

 

Continue reading Insect Pest and Crop Degree Day Update – May 26

Preventing Yield Loss from Flea Beetles

Flea beetles are a common crop pest of crucifers in Ontario and overwinter as adults near the soil surface in debris and stubble from the previous crop. They typically become active with the first extended period of warm weather in the early spring as the leaf litter begins to thaw. The beetles feed on weeds throughout the field and have the ability to fly on calm days and will attack brassica seedlings as they emerge or transplants as they are planted.

Females will begin laying eggs in soil for about 30 days. Flea beetle larvae will hatch from eggs 12 days later and feed on the root hairs and taproots of seedlings. Left unchecked, adults will feed on leaves of transplants and the larvae will burrowing into the plant near the juncture of the root and stem. Continue reading Preventing Yield Loss from Flea Beetles

Samples requested for clubroot survey

By Travis Cranmer, Vegetable Crops Specialist
OMAFRA

First appeared in ONvegetables in The Grower, April 2017.

Clubroot, caused by the soil-borne pathogen Plasmodiophora brassicae can cause yellowing, stunting, wilting and club-like roots on susceptible Brassica species including broccoli, cabbage, canola and cauliflower. Clubroot causes an estimated yield loss of 10-15% in Brassica crops worldwide and in severely infested fields a 30-100% yield loss can occur. There are different races of clubroot known as pathotypes and the resistance of many cultivars is pathotype dependent.

severe clubbing, six weeks after seeding
Figure 1. Pak choy with severe clubbing, six weeks after seeding.

Continue reading Samples requested for clubroot survey